A hydrodynamic device for use with a water vessel, such as a surfboard, to disrupt a flow of water under the water vessel. The hydrodynamic device comprises a channel member (12) fixed to an underside of the water vessel with an attachment means (14). The attachment means (14) may be a plurality of lugs (44) arranged to be received in corresponding recesses in the underside of the water vessel. In use, water flowing between the underside of the vessel and the channel member (12) passes from a high water pressure zone to a low water pressure zone thereby enhancing a forward thrust of the water vessel in the water.
